U.S. Pat. No. 2,641,485 discloses a valved pipe fitting comprising a rotationally-based valve plate 60. The valve plate 60 has lugs 64 through which apertures 66 are formed. The plate is biased by a coil spring having outwardly projecting arm portions 68,70 which engage the apertures 66 so that the coil spring also serves as a pivot element for the valve plate. The coil spring in said to operate in two modes, either biasing the valve plate 60 to a closed position or maintaining the same in a fully open position.
To applicant's knowledge, the only reference that discloses a check valve of the above description is U.S. Pat. No. 4,964,422 Ball et al.
This invention addresses two concerns presented by the structure illustrated in the '422 patent. The first concern is that the rack and pinion arrangement disclosed therein raises the potential for mechanical binding. The second concern is that the use of a pilot valve may be undesirable in many applications for two reasons. The first reason is that in applications which do not permit leakage, a sealing arrangement must be provided for the pilot valve as well as the main valve. The second reason is that in applications characterized by high back-pressure, the pilot valve may (depending on its design and composition) be closed violently, thus presenting the additional concerns of wear, damage, and noise.